Using a Frequency Error Estimate of a First Radio Access Technology (RAT) for a Second RAT

ABSTRACT

Using a frequency error estimate (FEE) of a first RAT for a second RAT. The UE may include a first radio which supports, e.g., simultaneously, a first radio access technology (RAT) and a second RAT. The first radio may use a lesser frequency of sleep and wake-up cycles when operating according to the first RAT than when operating according to the second RAT. The UE may perform a FEE associated with the first RAT. Accordingly, the UE may skip an FEE associated with the second RAT based on performing the FEE associated with the first RAT.

PRIORITY INFORMATION

The present application claims benefit of priority of U.S. ProvisionalApplication Ser. No. 61/948,305, titled “Improved Synchronization BeaconDetection”, whose inventor is Li Su, which was filed on Mar. 5, 2014,and which is hereby incorporated by reference in its entirety as thoughfully and completely set forth herein.

FIELD OF THE INVENTION

The present application relates to wireless devices, and moreparticularly to a system and method for providing improved performanceand/or reduced power consumption in wireless devices that supportmultiple radio access technologies (RATs).

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. Further,wireless communication technology has evolved from voice-onlycommunications to also include the transmission of data, such asInternet and multimedia content. Therefore, improvements are desired inwireless communication. In particular, the large amount of functionalitypresent in a user equipment (UE), e.g., a wireless device such as acellular phone, can place a significant strain on the battery life ofthe UE. Further, where a UE is configured to support multiple radioaccess technologies (RATs), certain performance degradations can occuron one or more of the RATs, such as due to tune-away operations of theother RAT. As a result, techniques are desired which provide powersavings and/or improved performance in such wireless UE devices.

New and improved cellular radio access technologies (RATs) are sometimesdeployed in addition to existing RATs. For example, networksimplementing Long Term Evolution (LTE) technology, developed andstandardized by the Third Generation Partnership Project (3GPP), arecurrently being deployed. LTE and other newer RATs often support fasterdata rates than networks utilizing legacy RATs, such as various secondgeneration (2G) and third generation (3G) RATs.

However, in some deployments, LTE and other new RATs may not fullysupport some services that can be handled by legacy networks.Accordingly, LTE networks are often co-deployed in overlapping regionswith legacy networks and UE devices may transition between RATs asservices or coverage may require. For example, in some deployments, LTEnetworks are not capable of supporting voice calls. Thus, for examplewhen a UE device receives or initiates a circuit switched voice callwhile connected to an LTE network that does not support voice calls, theUE device can transition to a legacy network, such as one which uses aGSM (Global System for Mobile Communications) RAT or a “1X” (CodeDivision Multiple Access 2000 (CDMA2000) 1X) RAT that supports voicecalls, among other possibilities.

Some UE devices use a single radio to support operation on multiplecellular RATs. For example, some UE devices use a single radio tosupport operation on both LTE and GSM networks. The use of a singleradio for multiple RATs makes transitioning between networks, such as inresponse to a page message for an incoming voice call or circuitswitched service, more complex. In addition, the use of a single radiofor multiple RATs presents certain power usage and performance issues.

For example, in such systems the UE may periodically tune from the firstnetwork, using a more advanced RAT, to the second network, using alegacy RAT, e.g., to listen to a paging channel for a voice call.However, such tune-away operations from a more advanced RAT, such asLTE, to a legacy RAT, such as GSM, can result in increased powerconsumption and/or performance degradation of the LTE network.

Therefore, it would be desirable to provide improved performance andpower consumption in wireless communication systems where a UE devicesuse a single radio to support operation on multiple cellular RATs.

SUMMARY OF THE INVENTION

Embodiments described herein relate to a User Equipment (UE) device andassociated method for performing detection of a synchronization beacon.The UE may include a first radio which supports, e.g., simultaneously, afirst radio access technology (RAT) and a second RAT. The UE may performtransmission according to the first RAT on the first radio with a basestation. The UE may receive a request to perform a tune-away to detect asynchronization beacon on the second RAT. The synchronization beacon mayrepetitively occur in successive first time periods. The UE mayrepeatedly perform a search for the synchronization beacon in differentsub-portions over successive first time periods. The search may berepeatedly performed until the synchronization beacon is located in arespective sub-portion of one of the successive time periods.

Embodiments described herein relate to a User Equipment (UE) device andassociated method for using a frequency error estimate of a first RATfor a second RAT. A first radio of the UE may be operated according to afirst radio access technology (RAT) and a second RAT. The first radiomay have a lesser frequency of sleep and wake-up cycles when operatingaccording to the first RAT than when operating according to the secondRAT. The first radio may use a first clock for each of the first RAT andthe second RAT, and the first clock may operate based on an oscillatorin the UE. When the radio is operating according to the first RAT, aftera plurality of cycles of sleep and wake-up, the UE may perform afrequency error estimate (FEE) of the first clock signal and adjust thefirst clock based on the frequency error estimate. The radio operatingaccording to the first RAT performing the FEE and adjusting the firstclock may operate to reduce a frequency of the radio performing a FEEand adjusting the first clock when operating according to the secondRAT.

This Summary is provided for purposes of summarizing some exemplaryembodiments to provide a basic understanding of aspects of the subjectmatter described herein. Accordingly, the above-described features aremerely examples and should not be construed to narrow the scope orspirit of the subject matter described herein in any way. Otherfeatures, aspects, and advantages of the subject matter described hereinwill become apparent from the following Detailed Description, Figures,and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the embodiments is considered inconjunction with the following drawings.

FIG. 1 illustrates an example user equipment (UE) according to oneembodiment;

FIG. 2 illustrates an example wireless communication system where a UEcommunicates with two base stations using two different RATs;

FIG. 3 is an example block diagram of a base station, according to oneembodiment;

FIG. 4 is an example block diagram of a UE, according to one embodiment;

FIGS. 5A and 5B are example block diagrams of wireless communicationcircuitry in the UE, according to one embodiment;

FIG. 6 is a flowchart diagram illustrating an exemplary method forperforming intermittent synchronization detection;

FIG. 7 is an exemplary timing diagram corresponding to one embodiment ofFIG. 6; and

FIG. 8 is a flowchart diagram illustrating an exemplary method for usinga frequency error estimate of a first RAT for a second RAT.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS Acronyms

The following acronyms are used in the present disclosure.

3GPP: Third Generation Partnership Project

3GPP2: Third Generation Partnership Project 2

GSM: Global System for Mobile Communications

UMTS: Universal Mobile Telecommunications System

LTE: Long Term Evolution

RAT: Radio Access Technology

TX: Transmit

RX: Receive

Terms

The following is a glossary of terms used in the present application:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks, or tape device; a computer system memoryor random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, RambusRAM, etc.; a non-volatile memory such as a Flash, magnetic media, e.g.,a hard drive, or optical storage; registers, or other similar types ofmemory elements, etc. The memory medium may include other types ofmemory as well or combinations thereof. In addition, the memory mediummay be located in a first computer system in which the programs areexecuted, or may be located in a second different computer system whichconnects to the first computer system over a network, such as theInternet. In the latter instance, the second computer system may provideprogram instructions to the first computer for execution. The term“memory medium” may include two or more memory mediums which may residein different locations, e.g., in different computer systems that areconnected over a network. The memory medium may store programinstructions (e.g., embodied as computer programs) that may be executedby one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), personal communication device, smart phone, televisionsystem, grid computing system, or other device or combinations ofdevices. In general, the term “computer system” can be broadly definedto encompass any device (or combination of devices) having at least oneprocessor that executes instructions from a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™,iPhone™), laptops, PDAs, portable Internet devices, music players, datastorage devices, other handheld devices, as well as wearable devicessuch as wrist-watches, headphones, pendants, earpieces, etc. In general,the term “UE” or “UE device” can be broadly defined to encompass anyelectronic, computing, and/or telecommunications device (or combinationof devices) which is easily transported by a user and capable ofwireless communication.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIG. 1—User Equipment

FIG. 1 illustrates an example user equipment (UE) 106 according to oneembodiment. The term UE 106 may be any of various devices as definedabove. UE device 106 may include a housing 12 which may be constructedfrom any of various materials. UE 106 may have a display 14, which maybe a touch screen that incorporates capacitive touch electrodes. Display14 may be based on any of various display technologies. The housing 12of the UE 106 may contain or comprise openings for any of variouselements, such as home button 16, speaker port 18, and other elements(not shown), such as microphone, data port, and possibly various othertypes of buttons, e.g., volume buttons, ringer button, etc.

The UE 106 may support multiple radio access technologies (RATs). Forexample, UE 106 may be configured to communicate using any of variousRATs such as two or more of Global System for Mobile Communications(GSM), Universal Mobile Telecommunications System (UMTS), Code DivisionMultiple Access (CDMA) (e.g., CDMA2000 1XRTT or other CDMA radio accesstechnologies), Long Term Evolution (LTE), Advanced LTE, and/or otherRATs. For example, the UE 106 may support at least two radio accesstechnologies such as LTE and GSM. Various different or other RATs may besupported as desired.

The UE 106 may comprise one or more antennas. The UE 106 may alsocomprise any of various radio configurations, such as variouscombinations of one or more transmitter chains (TX chains) and one ormore receiver chains (RX chains). For example, the UE 106 may comprise aradio that supports two or more RATs. The radio may comprise a single TX(transmit) chain and a single RX (receive) chain. Alternatively, theradio may comprise a single TX chain and two RX chains, e.g., thatoperate on the same frequency. In another embodiment, the UE 106comprises two or more radios, i.e., two or more TX/RX chains (two ormore TX chains and two or more RX chains).

In the embodiment described herein, the UE 106 comprises two antennaswhich communicate using two or more RATs. For example, the UE 106 mayhave a pair of cellular telephone antennas coupled to a single radio orshared radio. The antennas may be coupled to the shared radio (sharedwireless communication circuitry) using switching circuits and otherradio-frequency front-end circuitry. For example, the UE 106 may have afirst antenna that is coupled to a transceiver or radio, i.e., a firstantenna that is coupled to a transmitter chain (TX chain) fortransmission and which is coupled to a first receiver chain (RX chain)for receiving. The UE 106 may also comprise a second antenna that iscoupled to a second RX chain. The first and second receiver chains mayshare a common local oscillator, which means that both of the first andsecond receiver chains tune to the same frequency. The first and secondreceiver chains may be referred to as the primary receiver chain (PRX)and the diversity receiver chain (DRX).

In one embodiment, the PRX and DRX receiver chains operate as a pair andtime multiplex among two or more RATs, such as LTE and one or more otherRATs such as GSM or CDMA1x. In the primary embodiment described hereinthe UE 106 comprises one transmitter chain and two receiver chains (PRXand DRX), wherein the transmitter chain and the two receiver chains(acting as a pair) time multiplex between two (or more) RATs, such asLTE and GSM.

Each antenna may receive a wide range of frequencies such as from 600MHz up to 3 GHz. Thus, for example, the local oscillator of the PRX andDRX receiver chains may tune to a specific frequency such as an LTEfrequency band, where the PRX receiver chain receives samples fromantenna 1 and the DRX receiver chain receives samples from antenna 2,both on the same frequency (since they use the same local oscillator).The wireless circuitry in the UE 106 can be configured in real timedepending on the desired mode of operation for the UE 106. In theexample embodiment described herein, the UE 106 is configured to supportLTE and GSM radio access technologies.

FIG. 2—Communication System

FIG. 2 illustrates an exemplary (and simplified) wireless communicationsystem. It is noted that the system of FIG. 2 is merely one example of apossible system, and embodiments may be implemented in any of varioussystems, as desired.

As shown, the exemplary wireless communication system includes basestations 102A and 102B which communicate over a transmission medium withone or more user equipment (UE) devices, represented as UE 106. The basestations 102 may be base transceiver stations (BTS) or cell sites, andmay include hardware that enables wireless communication with the UE106. Each base station 102 may also be equipped to communicate with acore network 100. For example, base station 102A may be coupled to corenetwork 100A, while base station 102B may be coupled to core network100B. Each core network may be operated by a respective cellular serviceprovider, or the plurality of core networks 100A may be operated by thesame cellular service provider. Each core network 100 may also becoupled to one or more external networks (such as external network 108),which may include the Internet, a Public Switched Telephone Network(PSTN), and/or any other network. Thus, the base stations 102 mayfacilitate communication between the UE devices 106 and/or between theUE devices 106 and the networks 100A, 100B, and 108.

The base stations 102 and the UEs 106 may be configured to communicateover the transmission medium using any of various radio accesstechnologies (“RATs”, also referred to as wireless communicationtechnologies or telecommunication standards), such as GSM, UMTS (WCDMA),LTE, LTE Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD,eHRPD), IEEE 802.11 (WLAN or Wi-Fi), IEEE 802.16 (WiMAX), etc.

Base station 102A and core network 100A may operate according to a firstRAT (e.g., LTE) while base station 102B and core network 100B mayoperate according to a second (e.g., different) RAT (e.g., GSM, CDMA2000 or other legacy or circuit switched technologies). The two networksmay be controlled by the same network operator (e.g., cellular serviceprovider or “carrier”), or by different network operators, as desired.In addition, the two networks may be operated independently of oneanother (e.g., if they operate according to different RATs), or may beoperated in a somewhat coupled or tightly coupled manner.

Note also that while two different networks may be used to support twodifferent RATs, such as illustrated in the exemplary networkconfiguration shown in FIG. 2, other network configurations implementingmultiple RATs are also possible. As one example, base stations 102A and102B might operate according to different RATs but couple to the samecore network. As another example, multi-mode base stations capable ofsimultaneously supporting different RATs (e.g., LTE and GSM, LTE andCDMA2000 1xRTT, and/or any other combination of RATs) might be coupledto a core network that also supports the different cellularcommunication technologies. In one embodiment, the UE 106 may beconfigured to use a first RAT that is a packet-switched technology(e.g., LTE) and a second RAT that is a circuit-switched technology(e.g., GSM or 1xRTT).

As discussed above, UE 106 may be capable of communicating usingmultiple RATs, such as those within 3GPP, 3GPP2, or any desired cellularstandards. The UE 106 might also be configured to communicate usingWLAN, Bluetooth, one or more global navigational satellite systems(GNSS, e.g., GPS or GLONASS), one and/or more mobile televisionbroadcasting standards (e.g., ATSC-M/H or DVB-H), etc. Othercombinations of network communication standards are also possible.

Base stations 102A and 102B and other base stations operating accordingto the same or different RATs or cellular communication standards maythus be provided as a network of cells, which may provide continuous ornearly continuous overlapping service to UE 106 and similar devices overa wide geographic area via one or more radio access technologies (RATs).

FIG. 3—Base Station

FIG. 3 illustrates an exemplary block diagram of a base station 102. Itis noted that the base station of FIG. 3 is merely one example of apossible base station. As shown, the base station 102 may includeprocessor(s) 504 which may execute program instructions for the basestation 102. The processor(s) 504 may also be coupled to memorymanagement unit (MMU) 540, which may be configured to receive addressesfrom the processor(s) 504 and translate those addresses to locations inmemory (e.g., memory 560 and read only memory (ROM) 550) or to othercircuits or devices.

The base station 102 may include at least one network port 570. Thenetwork port 570 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above.

The network port 570 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106. In some cases, the network port 570may couple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devices106 serviced by the cellular service provider).

The base station 102 may include at least one antenna 534. The at leastone antenna 534 may be configured to operate as a wireless transceiverand may be further configured to communicate with UE devices 106 viaradio 530. The antenna 534 communicates with the radio 530 viacommunication chain 532. Communication chain 532 may be a receive chain,a transmit chain or both. The radio 530 may be configured to communicatevia various RATs, including, but not limited to, LTE, GSM, WCDMA,CDMA2000, etc.

The processor(s) 504 of the base station 102 may be configured toimplement part or all of the methods described herein, e.g., byexecuting program instructions stored on a memory medium (e.g., anon-transitory computer-readable memory medium). Alternatively, theprocessor 504 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit), or a combination thereof.

FIG. 4—User Equipment (UE)

FIG. 4 illustrates an example simplified block diagram of a UE 106. Asshown, the UE 106 may include a system on chip (SOC) 400, which mayinclude portions for various purposes. The SOC 400 may be coupled tovarious other circuits of the UE 106. For example, the UE 106 mayinclude various types of memory (e.g., including NAND flash 410), aconnector interface 420 (e.g., for coupling to a computer system, dock,charging station, etc.), the display 460, cellular communicationcircuitry 430 such as for LTE, GSM, etc., and short range wirelesscommunication circuitry 429 (e.g., Buletooth and WLAN circuitry). The UE106 may further comprise one or more smart cards 310 that comprise SIM(Subscriber Identity Module) functionality, such as one or more UICC(s)(Universal Integrated Circuit Card(s)) cards 310. The cellularcommunication circuitry 430 may couple to one or more antennas,preferably two antennas 435 and 436 as shown. The short range wirelesscommunication circuitry 429 may also couple to one or both of theantennas 435 and 436 (this connectivity is not shown for ease ofillustration).

As shown, the SOC 400 may include processor(s) 402 which may executeprogram instructions for the UE 106 and display circuitry 404 which mayperform graphics processing and provide display signals to the display460. The processor(s) 402 may also be coupled to memory management unit(MMU) 440, which may be configured to receive addresses from theprocessor(s) 402 and translate those addresses to locations in memory(e.g., memory 406, read only memory (ROM) 450, NAND flash memory 410)and/or to other circuits or devices, such as the display circuitry 404,cellular communication circuitry 430, short range wireless communicationcircuitry 429, connector I/F 420, and/or display 460. The MMU 440 may beconfigured to perform memory protection and page table translation orset up. In some embodiments, the MMU 440 may be included as a portion ofthe processor(s) 402.

In one embodiment, as noted above, the UE 106 comprises at least onesmart card 310, such as a UICC 310, which executes one or moreSubscriber Identity Module (SIM) applications and/or otherwise implementSIM functionality. The at least one smart card 310 may be only a singlesmart card 310, or the UE 106 may comprise two or more smart cards 310.Each smart card 310 may be embedded, e.g., may be soldered onto acircuit board in the UE 106, or each smart card 310 may be implementedas a removable smart card. Thus the smart card(s) 310 may be one or moreremovable smart cards (such as UICC cards, which are sometimes referredto as “SIM cards”), and/or the smart card(s) 310 may be one or moreembedded cards (such as embedded UICCs (eUICCs), which are sometimesreferred to as “eSIMs” or “eSIM cards”). In some embodiments (such aswhen the smart card(s) 310 include an eUICC), one or more of the smartcard(s) 310 may implement embedded SIM (eSIM) functionality; in such anembodiment, a single one of the smart card(s) 310 may execute multipleSIM applications. Each of the smart card(s) 310 may include componentssuch as a processor and a memory; instructions for performing SIM/eSIMfunctionality may be stored in the memory and executed by the processor.In one embodiment, the UE 106 may comprise a combination of removablesmart cards and fixed/non-removable smart cards (such as one or moreeUICC cards that implement eSIM functionality), as desired. For example,the UE 106 may comprise two embedded smart cards 310, two removablesmart cards 310, or a combination of one embedded smart card 310 and oneremovable smart card 310. Various other SIM configurations are alsocontemplated.

As noted above, in one embodiment, the UE 106 comprises two or moresmart cards 310, each implementing SIM functionality. The inclusion oftwo or more SIM smart cards 310 in the UE 106 may allow the UE 106 tosupport two different telephone numbers and may allow the UE 106 tocommunicate on corresponding two or more respective networks. Forexample, a first smart card 310 may comprise SIM functionality tosupport a first RAT such as LTE, and a second smart card 310 maycomprise SIM functionality to support a second RAT such as GSM. Otherimplementations and RATs are of course possible. Where the UE 106comprises two smart cards 310, the UE 106 may support Dual SIM DualActive (DSDA) functionality. The DSDA functionality may allow the UE 106to be simultaneously connected to two networks (and use two differentRATs) at the same time. The DSDA functionality may also allow the UE 106may to simultaneously receive voice calls or data traffic on eitherphone number. In another embodiment, the UE 106 supports Dual SIM DualStandby (DSDS) functionality. The DSDS functionality may allow either ofthe two smart cards 310 in the UE 106 to be on standby waiting for avoice call and/or data connection. In DSDS, when a call/data isestablished on one SIM 310, the other SIM 310 is no longer active. Inone embodiment, DSDx functionality (either DSDA or DSDS functionality)may be implemented with a single smart card (e.g., a eUICC) thatexecutes multiple SIM applications for different carriers and/or RATs.

As noted above, the UE 106 may be configured to communicate wirelesslyusing multiple radio access technologies (RATs). As further noted above,in such instances, the cellular communication circuitry (radio(s)) 430may include radio components which are shared between multiple RATSand/or radio components which are configured exclusively for useaccording to a single RAT. Where the UE 106 comprises at least twoantennas, the antennas 435 and 436 may be configurable for implementingMIMO (multiple input multiple output) communication.

As described herein, the UE 106 may include hardware and softwarecomponents for implementing features for communicating using two or moreRATs, such as those described herein. The processor 402 of the UE device106 may be configured to implement part or all of the features describedherein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium).Alternatively (or in addition), processor 402 may be configured as aprogrammable hardware element, such as an FPGA (Field Programmable GateArray), or as an ASIC (Application Specific Integrated Circuit).Alternatively (or in addition) the processor 402 of the UE device 106,in conjunction with one or more of the other components 400, 404, 406,410, 420, 430, 435, 440, 450, 460 may be configured to implement part orall of the features described herein.

FIGS. 5A and 5B—UE Transmit/Receive Logic

FIG. 5A illustrates a portion of UE 106 according to one embodiment. Asshown, UE 106 may comprise control circuitry 42 that is configured tostore and execute control code for implementing control algorithms inthe UE 106. Control circuitry 42 may include storage and processingcircuitry 28 (e.g., a microprocessor, memory circuits, etc.) and mayinclude baseband processor integrated circuit 58. Baseband processor 58may form part of wireless circuitry 34 and may include memory andprocessing circuits (i.e., baseband processor 58 may be considered toform part of the storage and processing circuitry of UE 106). Basebandprocessor 58 may comprise software and/or logic for handling variousdifferent RATs, such as GSM logic 72 and LTE logic 74, among others.

Baseband processor 58 may provide data to storage and processingcircuitry 28 (e.g., a microprocessor, nonvolatile memory, volatilememory, other control circuits, etc.) via path 48. The data on path 48may include raw and processed data associated with UE cellularcommunications and operations, such as cellular communication data,wireless (antenna) performance metrics for received signals, informationrelated to tune-away operations, information related to pagingoperations, etc. This information may be analyzed by storage andprocessing circuitry 28 and/or processor 58 and, in response, storageand processing circuitry 28 (or, if desired, baseband processor 58) mayissue control commands for controlling wireless circuitry 34. Forexample, storage and processing circuitry 28 may issue control commandson path 52 and path 50 and/or baseband processor 58 may issue commandson path 46 and path 51.

Wireless circuitry 34 may include radio-frequency transceiver circuitrysuch as radio-frequency transceiver circuitry 60 and radio-frequencyfront-end circuitry 62. Radio-frequency transceiver circuitry 60 mayinclude one or more radio-frequency transceivers. In the embodimentshown radio-frequency transceiver circuitry 60 comprises transceiver(TX) chain 59, receiver (RX) chain 61 and RX chain 63. As noted above,the two RX chains 61 and 63 may be a primary RX chain 61 and a diversityRX chain 63. The two RX chains 61 and 63 may be connected to the samelocal oscillator (LO) and thus may operate together at the samefrequency for MIMO operations. Thus the TX chain 59 and the two RXchains 61 and 63 may be considered, along with other necessarycircuitry, as a single radio. Other embodiments are of coursecontemplated. For example, the radio-frequency transceiver circuitry 60may comprise only a single TX chain and only a single RX chain, also asingle radio embodiment. Thus the term “radio” may be defined to havethe broadest scope of its ordinary and accepted meaning, and comprisesthe circuitry normally found in a radio, including either a single TXchain and a single RX chain or a single TX chain and two (or more) RXchains, e.g., connected to the same LO. The term radio may encompass thetransmit and receive chains discussed above and may also include digitalsignal processing coupled to the radio frequency circuitry (e.g., thetransmit and receive chains) associated with performing wirelesscommunication. As one example, the transmit chain may include suchcomponents as amplifier, mixer, filter, and digital analog converter.Similarly, the receive chain(s) may include, e.g., such components asamplifier, mixer, filter, and analog to digital converter. As mentionedabove, multiple receive chains may share a LO, although in otherembodiments, they may comprise their own LO. Wireless communicationcircuitry may encompass a larger set of components, e.g., including oneor more radios of the UE (transmit/receive chains and/or digital signalprocessing), baseband processors, etc. The term “cellular wirelesscommunication circuitry” includes various circuitry for performingcellular communication, e.g., as opposed to other protocols that are notcellular in nature, such as Bluetooth. Certain embodiments of theinvention described herein may operate to improve performance when asingle radio (i.e., a radio with a single TX chain and single RX chain;or a radio with a single TX chain and two RX chains, where the two RXchains are connected to the same LO) supports multiple RATs.

As shown in FIG. 5B, the radio-frequency transceiver circuitry 60 mayalso comprise two or more TX chains and two or more RX chains. Forexample, FIG. 5B shows an embodiment with a first radio 57 comprising TXchain 59 and RX chain 61 and a second radio 63 comprising a first TXchain 65 and a second TX chain 67. Embodiments are also contemplatedwhere additional TX/RX receive chains may be included in the embodimentof FIG. 5A, i.e., in addition to the one TX chain 59 and two RX chains61 and 63 shown. In these embodiments that have multiple TX and RXchains, when only one radio is currently active, e.g., the second radiois turned off to save power, certain embodiments of the inventiondescribed herein may operate to improve performance of the single activeradio when it supports multiple RATs.

Baseband processor 58 may receive digital data that is to be transmittedfrom storage and processing circuitry 28 and may use path 46 andradio-frequency transceiver circuitry 60 to transmit correspondingradio-frequency signals. Radio-frequency front end 62 may be coupledbetween radio-frequency transceiver 60 and antennas 40 and may be usedto convey the radio-frequency signals that are produced byradio-frequency transceiver circuitry 60 to antennas 40. Radio-frequencyfront end 62 may include radio-frequency switches, impedance matchingcircuits, filters, and other circuitry for forming an interface betweenantennas 40 and radio-frequency transceiver 60.

Incoming radio-frequency signals that are received by antennas 40 may beprovided to baseband processor 58 via radio-frequency front end 62,paths such as paths 54 and 56, receiver circuitry in radio-frequencytransceiver 60, and paths such as path 46. Path 54 may, for example, beused in handling signals associated with transceiver 57, whereas path 56may be used in handling signals associated with transceiver 63. Basebandprocessor 58 may convert received signals into digital data that isprovided to storage and processing circuitry 28. Baseband processor 58may also extract information from received signals that is indicative ofsignal quality for the channel to which the transceiver is currentlytuned. For example, baseband processor 58 and/or other circuitry incontrol circuitry 42 may analyze received signals to produce variousmeasurements, such as bit error rate measurements, measurements on theamount of power associated with incoming wireless signals, strengthindicator (RSSI) information, received signal code power (RSCP)information, reference symbol received power (RSRP) information,signal-to-interference ratio (SINR) information, signal-to-noise ratio(SNR) information, channel quality measurements based on signal qualitydata such as Ec/Io or Ec/No data, etc.

Radio-frequency front end 62 may include switching circuitry. Theswitching circuitry may be configured by control signals received fromcontrol circuitry 42 (e.g., control signals from storage and processingcircuitry 28 via path 50 and/or control signals from baseband processor58 via path 51). The switching circuitry may include a switch (switchcircuit) that is used to connect TX and RX chain(s) to antennas 40A and40B. Radio-frequency transceiver circuitry 60 may be configured bycontrol signals received from storage and processing circuitry over path52 and/or control signals received from baseband processor 58 over path46.

The number of antennas that are used may depend on the operating modefor UE 106. For example, as shown in FIG. 5A, in normal LTE operations,antennas 40A and 40B may be used with respective receivers 61 and 63 toimplement a receive diversity scheme, such as for MIMO operations. Withthis type of arrangement, two LTE data streams may be simultaneouslyreceived and processed using baseband processor 58. When it is desiredto monitor a GSM paging channel for incoming GSM pages, one or both ofthe antennas may be temporarily used in receiving GSM paging channelsignals.

Control circuitry 42 may be used to execute software for handling morethan one radio access technology. For example, baseband processor 58 mayinclude memory and control circuitry for implementing multiple protocolstacks such as a GSM protocol stack 72 and an LTE protocol stack 74.Thus, protocol stack 72 may be associated with a first radio accesstechnology such as GSM (as an example), and protocol stack 74 may beassociated with a second radio access technology such as LTE (as anexample). During operation, UE 106 may use GSM protocol stack 72 tohandle GSM functions and may use LTE protocol stack 74 to handle LTEfunctions. Additional protocol stacks, additional transceivers,additional antennas 40, and other additional hardware and/or softwaremay be used in UE 106 if desired. The arrangement of FIGS. 5A and 5B ismerely illustrative. In one embodiment, one or both of the protocolstacks may be configured to implement the methods described in theflowcharts below.

In one embodiment of FIG. 5A (or 5B), the cost and complexity of UE 106may be minimized by implementing the wireless circuitry of FIG. 5A (or5B) using an arrangement in which baseband processor 58 andradio-transceiver circuitry 60 are used to support both LTE and GSMtraffic.

The GSM radio access technology may generally be used to carry voicetraffic, whereas the LTE radio access technology may generally be usedto carry data traffic. To ensure that GSM voice calls are notinterrupted due to LTE data traffic, GSM operations may take priorityover LTE operations. To ensure that operations such as monitoring a GSMpaging channel for incoming paging signals do not unnecessarily disruptLTE operations, control circuitry 42 can, whenever possible, configurethe wireless circuitry of UE 106 so that wireless resources are sharedbetween LTE and GSM functions.

When a user has an incoming GSM call, the GSM network may send UE 106 apaging signal (sometimes referred to as a page) on the GSM pagingchannel using base station 102. When UE 106 detects an incoming page, UE106 can take suitable actions (e.g., call establishment procedures) toset up and receive the incoming GSM call. Pages are typically sentseveral times at fixed intervals by the network, so that devices such asUE 106 will have multiple opportunities to successfully receive a page.

Proper GSM page reception may require that the wireless circuitry of UE106 be periodically tuned to the GSM paging channel, referred to as atune-away operation. If the transceiver circuitry 60 fails to tune tothe GSM paging channel or if the GSM protocol stack 72 in basebandprocessor 58 fails to monitor the paging channel for incoming pages, GSMpages will be missed. On the other hand, excessive monitoring of the GSMpaging channel may have an adverse impact on an active LTE data session.Embodiments of the invention may comprise improved methods for handlingtune-away operations, as described below.

In some embodiments, in order for the UE 106 to conserve power, the GSMand LTE protocol stacks 72 and 74 may support idle mode operations.Also, one or both of the protocol stacks 72 and 74 may support adiscontinuous reception (DRX) mode and/or a connected discontinuousreception (CDRX) mode. DRX mode refers to a mode which powers down atleast a portion of UE circuitry when there is no data (or voice) to bereceived. In DRX and CRDX modes, the UE 106 synchronizes with the basestation 102 and wakes up at specified times or intervals to listen tothe network. DRX is present in several wireless standards such as UMTS,LTE (Long-term evolution), WiMAX, etc. The terms “idle mode”, “DRX” and“CDRX” are explicitly intended to at least include the full extent oftheir ordinary meaning, and are intended to encompass similar types ofmodes in future standards.

Synchronization Beacon Detection

As discussed above, a UE may use a single radio (e.g., having a singletransmit chain and a single receive chain, although a single transmitchain a double receive chains are also envisioned) to communicate usingtwo different RATs. For example, the UE may use a single radio tocommunicate using a first RAT and may periodically tune away in order toperform various actions for a second RAT, such as page decoding,measurement, synchronization, etc. In this example, the UE may beconsidered as maintaining a connection to both RATs using the sameradio, even though it may only communicate using one RAT at a time. Notethat the radio may be the single cellular radio for the UE or may be oneof a plurality of cellular radios. In a multiple radio embodiment, andone of the cellular radios may be used for time-sharing of the first RATand the second RAT. Additionally, the UE may implement dual SIM dualactive (DSDA) and/or dual SIM dual standby (DSDS), as desired.

In one embodiment, the first RAT may be LTE and the second RAT may beGSM, although other combinations of RATs are envisioned. In some cases,it may be typical to tune away periodically in order to performsynchronization for the second RAT (e.g., for neighboring base stationsof the current base station of the second RAT). In the following, thefirst RAT may be described as LTE and the second RAT may be described asGSM, but any of these descriptions may apply to other RATs, as desired.

In comparison to CDMA 2000 1x, SRLTE for GSM may have significantdifferences. For example, GSM tune-away (e.g., for page decoding) may be10 times more frequent (e.g., at least once per 470 ms) than 1x tune-waywhich is once per 5.21 s. Additionally, in most cases, the duration ofeach GSM tune-away may be very short, e.g., 10-20 milliseconds, while inmost cases duration of 1x tune-away may be 90-100 milliseconds.

However, there may be situations where synchronization procedures forGSM may take a significant amount of time, which may reduce LTEthroughput because the LTE network may interpret the tune-away of theradio to GSM as a deep fading event and reduce coding and modulationschemes and/or resource block allocation. As one example, in an areawhere GSM coverage is weak, or many GSM cells clustered (e.g., intypical urban area), GSM tone detection for searching many new or lostGSM cells may take a long time to complete. For example, to detect a GSMcell, the UE may need to receive radio frequency signals of at least 10GSM frames (total 46 ms) continuously, and search for the location ofthe FCCH slot or burst within those 10 frames. In addition, typically toavoid missing detection of the FCCH slot, multiple (e.g., 2 or 3)10-GSM-frames are needed. However, as mentioned above, tuning away fromLTE for this period of time may incur significant throughput issues forLTE when using a radio for both LTE and GSM. For example, the LTEnetwork may dramatically throttle grant/MCS allocation if a largecluster of missing LTE frames occur in a row or over a short period oftime.

Accordingly, some of these issues may be resolved by distributing theGSM tone detection from a long tune away to multiple shorter tune awaysover a longer period of time. For example, by distributing the tonedetection, the LTE network may observe multiple quick fading over alonger time rather than continuous deep fading, which may result in alower average block error rate (BLER). This lower BLER may avoidtriggering a dramatic grant or MCS drop for LTE.

In one embodiment, for lower GSM received signal strength indicators(RSSIs) (e.g., less than or equal to −90 dBm), the first 10-GSM-frameperiod may be sampled continuously, FCCH tone detection may be performedon the samples, and then reconfirmed for the 2nd and 3rd 10-GSM-frameperiods. However, to confirm, the UE may read different 10 ms longsamples from each 10-GSM-frame period within a set of five 10-GSM-fameperiods. Then, these four pieces of 10 millisecond samples may becombined to form one 50 millisecond sample, which can be used for tonedetection, e.g., as a single 10-GSM period.

For higher GSM RSSI, even the 1st 10-GSM frame period samples can beread across multiple 10-GSM-frame periods, if desired.

Additionally, tone detection can be pipelined. For example, followingthe 10 ms samples from above, tone detection may be performed on eachavailable received 10 ms samples, while the next 10 millisecond samplesis being received or sampled. Accordingly, when all samples arecollected, the final tone detection can be used as a quick confirmationof the tone detection already performed on the 10 millisecond samples.

Following these embodiments, there may be a dramatic improvement in LTEthroughput for this situation, e.g., degradation may be reduced from40-50% to below 20%.

FIG. 6—Intermittent Synchronization Beacon Detection

FIG. 6 is a flowchart diagram illustrating a method for performingintermittent synchronization beacon detection. The method may beperformed by a UE device (such as UE 106) that uses a first radio forboth a first RAT and a second RAT (e.g., LTE and GSM, although othercombinations of RATs are envisioned). The method shown in FIG. 6 may beused in conjunction with any of the systems or devices shown in theabove Figures, among other devices. In various embodiments, some of themethod elements shown may be performed concurrently, in a differentorder than shown, or may be omitted. Note also that additional methodelements may also be performed as desired. The method may be performedas follows.

As shown, in 602, the UE may communicate using a first RAT using thefirst radio. For example, the UE may perform data communication usingthe first RAT, or more generally, the first radio may be currently usedfor first RAT communication.

In 604, the UE may receive a request to perform synchronization, e.g.,for neighboring base stations, of the second RAT. In order to performsynchronization, the UE may perform synchronization beacon detection(e.g., tone detection, such as detecting an FCCH burst for GSM). Asdiscussed above, the synchronization beacon may be repeatedlytransmitted in a periodic manner. For example, the synchronizationbeacon may be transmitted once during each repeated time length or timeperiod (referred to as a “first time period” or “first time length”regarding FIG. 6, such as every 10 GSM frames in GSM embodiments).

In 606, the UE may repeatedly perform a search for the synchronizationbeacon in different sub-portions of the first time period oversuccessive transmissions. More specifically, the UE may search for thesynchronization beacon across the first time period, but may not have tosearch a single instance of the first time period (in other words, thesearch may occur across multiple first time periods). As a particularexample, the UE may search a first n frames of the first time period ina first instance of the time period, the second n frames in a secondinstance of the time period, etc., until the entire time period hassearched, over a plurality of instances of the time period.

FIG. 7 illustrates an exemplary timing diagram showing the differencebetween a continuous detection and an intermittent detection of thesynchronization beacon. In particular, 700 illustrates a continuousdetection of the synchronization beacon. In this instance, the UE mayperform synchronization beacon detection across the first 10 frames(e.g., corresponding to a GSM embodiment). As shown, the FCCH beacon maybe transmitted between the 6^(th) and 8^(th) frame of the 10 frames,each 10 frames (e.g., an exemplary first time period discussed above).In contrast, 750 shows an exemplary intermittent detection. In thisexample, the UE may perform sampling or measurement for only 1 frame ofeach 10 frames, and combine those samples together to performsynchronization beacon detection. In this example, the UE may sample thefirst frame of the first 10 frames, the second frame of the second 10frames, the third frame of the third 10 frames, etc., in order togenerate a “stitched together” 10 frame period, which may be used forsynchronization beacon detection (in this case, detection of the FCCHbeacon). As another example, 10 millisecond sampling may be performed,which may span across multiple frames, instead of the single framesshown in FIG. 7. In general, any desired sampling may be used, and thedescribed and illustrated sampling of FIG. 7 is exemplary only.

In one embodiment, the synchronization beacon detection may bepipelined, e.g., may include sampling a portion of the first time periodand performing synchronization beacon detection of that sample prior toperforming the next sample (although there may be other delays, such asperforming detection on a sample received two samples ago). In thisembodiment, it may be possible to detect the synchronization beaconwithout having to sample the entire first period. In one embodiment,once the synchronization beacon is detected, the search may be ended.

In some embodiments, upon detection of the synchronization beacon, aconfirmation of the synchronization beacon may be performed. Forexample, the location of the synchronization beacon may be sampled oneor more times in later first time periods to confirm the synchronizationbeacon. Alternatively, or additionally, the search may simply beconfirmed or performed across multiple instances of the first timeperiod (e.g., combining together more than a single first time periodamount, such as 10 frames for GSM).

In one embodiment, the method may use both continuous and intermittentdetection. For example, an initial continuous detection may beperformed, followed by intermittent detection for confirming thesynchronization beacon. As a specific example, for GSM, the 10 framesmay be continuously sampled initially, followed by detection of thesynchronization beacon within the sampled 10 frames. After thisdetection, confirmation of the synchronization beacon may be performedfor two additional 10 frame periods, but in an intermittent manner(e.g., where each sampled 10 frame period is formed from a plurality of10 frame periods). Alternatively, or additionally, the UE may simplyperform confirmation by sampling the particular frame(s) of the 10 frameperiod that correspond to the location of the detected synchronizationbeacon, rather than performing intermittent detection over the entire 10frame period.

In one embodiment, this continuous followed by intermittent detectionmay be performed when a channel quality indicator (e.g., signal qualityindicator, such as an RSSI, among other indicators) of the second RAT isbelow a threshold. When the channel quality indicator is above thethreshold, intermittent detection may be performed throughout, e.g., forboth initial detection and confirmation, without using continuousdetection. In one embodiment, the threshold may be an RSSI value ofapproximately −90 dBm. For example, this approximate value mayrange+/−10 dBm from −90 dBm, if desired.

During intermittent detection, the UE may alternate between using thefirst radio for the first RAT (e.g., for data communication) and usingthe first radio to perform the synchronization beacon search (andpotentially other activities, such as page detection) for the secondRAT. As a result, the UE may avoid deep fading conditions in the firstRAT due to a long tune away to perform continuous synchronization beacondetection in the second RAT, which may avoid significant throughput lossfor the first RAT.

Using Frequency Error Estimate of a First RAT for a Second RAT

As discussed above, a UE may use a single radio (e.g., having a singletransmit chain and a single receive chain) to communicate using twodifferent RATs. For example, the UE may use a single radio tocommunicate using a first RAT and may periodically tune away in order toperform various actions for a second RAT, such as page decoding,measurement, synchronization, etc. In this example, the UE may beconsidered as maintaining a connection to both RATs using the sameradio, even though it may only communicate using one RAT at a time. Notethat the radio may be the single cellular radio for the UE or may be oneof a plurality of cellular radios. In a multiple radio embodiment, andone of the cellular radios may be used for time-sharing of the first RATand the second RAT. Additionally, the UE may implement dual SIM dualactive (DSDA) and/or dual SIM dual standby (DSDS), as desired.

In one embodiment, the first RAT may be LTE and the second RAT may beGSM, although other combinations of RATs are envisioned. In some cases,it may be typical to tune away periodically in order to performsynchronization for the second RAT (e.g., for neighboring base stationsof the current base station of the second RAT).

In the following, the first RAT may be described as LTE and the secondRAT may be described as GSM, but any of these descriptions may apply toother RATs, as desired. The LTE DRX cycle may be approximately 1.28seconds. Additionally, the GSM DRX cycle may occur every 470milliseconds. GSM frequency Error Estimate (FEE) typically takes 200-500ms and may be performed after multiple cycles of GSM DRX sleep andwakeup. The FEE is generally performed because there are frequencyerrors from the crystal oscillator which is used when GSM sleeps (e.g.,the software stack associated with GSM, radio frequency circuitryassociated with GSM, and/or other portions of the UE). At wakeup, if thefrequency error is higher than a threshold and is not corrected, GSMTX/RX will be biased to a wrong frequency, and the network may not beable to decode the UE's transmission. Similarly, UE may not be able todecode network's response. Even though GSM FEE is not frequent (e.g.,typically occurring once per 10-50 s), once it occurs, it may have alarge impact on LTE performance for GSM-SRLTE or DSDS/DSDA. Inparticular, this extremely long tune away from LTE may dramatically dragdown LTE throughput performance.

Accordingly, reducing the number of times GSM FEE is performed mayimprove this performance, particularly for LTE, when both GSM and LTEare used via a same radio. The following embodiments may be useful inreducing the frequency or occurrences of GSM FEE:

In SRLTE with GSM, because LTE and GSM time-share the same radiofrequency circuitry (or at least a portion of the radio frequencycircuitry), they may also use the same crystal oscillator while asleep.Additionally, LTE also performs FEE after multiple cycles of LTE sleepand wakeup. Accordingly, when LTE is active, even though GSM hasmultiple cycles of sleep and wakeup, GSM does not need to do FEE itself,instead, GSM can directly use the FEE result for LTE (or the effects ofthe FEE from LTE may also address the need to perform FEE for GSM). Forexample, in these embodiments, when FEE is performed for LTE the timerassociated with performing GSM FEE may be reset, since the LTE FEE canbe used for the GSM FEE.

However, if LTE (e.g., the software stack associated with LTE, radiofrequency circuitry associated with LTE, and/or other portions of theUE) is sleeping, and if GSM FEE timer expires, which is the max time isreached when GSM hasn't perform FEE since the last FEE and sleep, GSMmay perform its FEE.

The above embodiments may limit GSM FEE occurrence to when LTE is insleep, and as a result, may almost eliminate the FEE long tune-awayimpact on LTE throughput performance. Thus, the above embodiments mayrestrict degradation down to access delay when LTE is wakeup from CDRXsleep.

FIG. 8—Using Frequency Error Estimate of a First RAT for a Second RAT

FIG. 8 is a flowchart diagram illustrating a method for using afrequency error estimate of a first RAT for a second RAT. The method ofFIG. 8 may be performed by a UE device (such as UE 106) that uses afirst radio for both the first RAT and the second RAT (e.g., LTE andGSM, although other combinations of RATs are envisioned). The methodshown in FIG. 8 may be used in conjunction with any of the systems ordevices shown in the above Figures, among other devices. In variousembodiments, some of the method elements shown may be performedconcurrently, in a different order than shown, or may be omitted. Notealso that additional method elements may also be performed as desired.The method may be performed as follows.

In 802, the UE may operate the first radio according to the first RAT.For example, a software stack associated with the first RAT mayperiodically use the first radio in performing communication using thefirst RAT. References to the first RAT performing actions or beingasleep may refer to this first RAT software stack being executed toperform those actions, or being dormant.

In 804, the UE may operate the first radio according to the second RAT.For example, similar to above, a software stack associated with thesecond RAT may periodically use the first radio in performingcommunication using the second Rat. References to the first RATperforming actions or being asleep may refer to this second softwarestack being executed to perform those actions, or being dormant.

While operating according to the first RAT, the first radio may have alesser frequency (or periodicity) of sleep and wake-up cycles than whileoperating according to the second RAT, which may have a greaterfrequency (or periodicity) of sleep and wake-up cycles. For example, thefirst RAT may have a cycle (e.g., a DRX cycle) that lasts 1.28 secondwhile the second RAT may have a cycle (e.g., a DRX cycle) that lasts 470milliseconds. Additionally, the first radio may use a first clock foroperating according to both of the first RAT and the second RAT. Forexample, the first clock may be used during sleep cycles for the firstRAT and may also be used during sleep cycles for the second RAT. Thefirst clock may operate based on an oscillator (e.g., a crystaloscillator) of the UE.

Periodically, for both the first RAT and the second RAT, a frequencyerror estimate (FEE) may be performed in order to ensure that the firstclock is within appropriate tolerance for communicating using the firstRAT and/or the second RAT, e.g., upon waking from sleep. However, sincethe first clock is shared between the first RAT and the second RAT, itmay be possible to use the results of the FEE for one of the RATs forthe other RAT, without having to perform the FEE for both RATs.

Accordingly, when the first radio is being used for both the first RATand the second RAT, an FEE of the first RAT may allow the second RAT toskip performing an FEE of the second RAT. For example, the first RAT maybe LTE and the second RAT may be GSM. In one embodiment, an FEE may beperformed for the first RAT (in this example, LTE) during operation(e.g., this FEE may be performed periodically, such according to an FEEtimer of the first RAT). For example, the FEE may be performed for thefirst RAT after multiple sleep and wake-up cycles associated with thefirst RAT, e.g., a predefined number of cycles.

During this period, the first radio may be used for both the first RATand the second RAT. The second RAT may also be configured toperiodically perform the FEE for the second RAT, e.g., according to itsown FEE timer. For example, the timer may be used to indicate when a FEEmay be performed for the second RAT. However, when the FEE for the firstRAT is performed, the need to perform the FEE for the second RAT may nolonger be necessary, e.g., since the results of the FEE may adjust thefirst clock or may used by the second RAT for adjusting the first clockor another clock, if desired. For example, in one embodiment, adjustingthe first clock based on the FEE of the first RAT may resolve any needto perform FEE and first clock adjustment for the second RAT. In oneembodiment, the timer for the second RAT may simply be reset uponperforming the FEE for the first RAT. Alternatively, any measurements oradjustments determined from the FEE of the first RAT may be usable formeasurements or adjustments for the second RAT, without having toperform a new FEE for the second RAT. Even further, if separate clocksare used for the first and second RATs, e.g., and they are based on asame oscillator, the FEE of the first RAT may be used to adjust theclock of the second RAT. Thus, in this embodiment, the results of theFEE of the first RAT may be used for the second RAT without performing aseparate FEE for the second RAT, which may significantly reduce orremove tune-aways of the first radio from the first RAT to the secondRAT for the purpose of performing FEE of the second RAT, which mayreduce throughput degradation of the first RAT.

Thus, in 806, an FEE for the first RAT may be performed, andaccordingly, an FEE for the second RAT may be able to be avoided, asdiscussed above.

Later, in 808, an FEE for the second RAT may be performed. In oneembodiment, the FEE for the second RAT may be performed in situationswhere the first RAT is asleep or has not been recently used and an FEEfor the first RAT was not recent enough. For example, if the first RATis asleep and a timer for performing FEE for the second RAT expires, theFEE may be performed for the second RAT.

Embodiments of the present invention may be realized in any of variousforms. For example, in some embodiments, the present invention may berealized as a computer-implemented method, a computer-readable memorymedium, or a computer system. In other embodiments, the presentinvention may be realized using one or more custom-designed hardwaredevices such as ASICs. In other embodiments, the present invention maybe realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE) may be configured to includea processor (or a set of processors) and a memory medium, where thememory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A method, comprising: at a user equipment device(UE) comprising a first radio, wherein the first radio is configurableto operate according to a first radio access technology (RAT) and asecond RAT: operating the first radio of the UE according to the firstRAT, wherein the first radio has a lesser frequency of sleep and wake-upcycles when operating according to the first RAT; operating the firstradio according to the second RAT, wherein the first radio has a greaterfrequency of sleep and wake-up cycles when operating according to thesecond RAT; wherein the first radio uses a first clock for each of thefirst RAT and the second RAT, wherein the first clock operates based onan oscillator in the UE; when the radio is operating according to thefirst RAT, after a plurality of cycles of sleep and wake-up for thefirst RAT, performing a frequency error estimate (FEE) of the firstclock and adjusting the first clock based on the FEE, wherein performingthe FEE and adjusting the first clock while operating according to thefirst RAT operates to reduce a frequency of the radio performing a FEEand adjusting the first clock when operating according to the secondRAT.
 2. The method of claim 1, further comprising: operating a secondRAT FEE timer which indicates upon expiry that a FEE and clockadjustment should be performed, wherein the second RAT FEE timer isreset upon performing the FEE of the first clock for the first RAT. 3.The method of claim 2, further comprising: wherein when the first RAT isin a sleep portion of its sleep and wake-up cycles upon expiry of thesecond RAT FEE timer, performing a FEE of the first clock in response tothe first RAT being in a sleep portion of its sleep and wake-up cyclesupon expiry of the second RAT FEE timer.
 4. The method of claim 1,further comprising: using the FEE of the first RAT to adjust the firstclock for the second RAT.
 5. The method of claim 1, wherein the firstradio uses the first clock for the first RAT during sleep cyclesassociated with the first RAT and for the second RAT during sleep cyclesassociated with the second RAT.
 6. The method of claim 1, wherein the UEcomprises only a single radio for performing cellular communication,wherein the first radio is the single radio.
 7. The method of claim 1,wherein the UE comprises two smart cards which are each configured toimplement SIM (Subscriber Identity Module) functionality, wherein the UEis configured to implement DSDA (Dual SIM Dual Active) functionalityusing the first radio.
 8. The method of claim 1, wherein the first RATcomprises long term evolution (LTE).
 9. The method of claim 1, whereinthe second RAT comprises global system for mobile communications (GSM).10. The method of claim 1, wherein the oscillator comprises a crystaloscillator.
 11. A user equipment device (UE) configured to performselective neighbor cell measurement, comprising: an oscillator; a firstradio coupled to the oscillator, wherein the first radio is configuredto perform communication using a first radio access technology (RAT) anda second RAT and maintain a connection to both the first RAT and thesecond RAT, and wherein the first radio uses the oscillator for both thefirst RAT and the second RAT; and one or more processors coupled to thefirst radio, wherein the one or more processors and the first radio areconfigured to: configure the first radio using first software associatedwith the first RAT; configure the first radio using second softwareassociated with the second RAT, wherein the first software operates thefirst radio with a lesser frequency of sleep and wake-up cycles for thefirst RAT than the second software operates the first radio for thesecond RAT; when the radio is configured using the first software andoperating according to the first RAT, the first software performing afrequency error estimate (FEE) of a first clock that is based on theoscillator and adjusting the first clock based on the FEE, wherein thefirst software performing the FEE operates to reduce a frequency of thesecond software performing a FEE.
 12. The UE of claim 11, wherein thefirst radio uses the first clock for both the first RAT and the secondRAT, wherein performing the FEE comprises adjusting the first clock. 13.The UE of claim 11, wherein the first radio uses the first clock duringsleep cycles associated with the first RAT and wherein the first radiouses the first clock during sleep cycles associated with the second RAT.14. The UE of claim 11, wherein the second software is configured tooperate a second RAT FEE timer which indicates upon expiry that a FEEshould be performed, wherein the second RAT FEE timer is reset uponperforming the FEE of the first clock for the first RAT.
 15. The UE ofclaim 14, wherein when the first RAT is in a sleep portion of its sleepand wake-up cycles upon expiry of the second RAT FEE timer, the secondsoftware is configured to perform a FEE in response to the first RATbeing in a sleep portion of its sleep and wake-up cycles upon expiry ofthe second RAT FEE timer.
 16. The UE of claim 11, wherein the secondsoftware is configured to use results of the FEE to adjust a clock forthe second RAT.
 17. The UE of claim 11, wherein the UE comprises only asingle radio for performing cellular communication, wherein the firstradio is the single radio.
 18. The UE of claim 11, wherein the UEcomprises two smart cards which are each configured to implement SIM(Subscriber Identity Module) functionality, wherein the UE is configuredto implement DSDA (Dual SIM Dual Active) functionality using the firstradio.
 19. The UE of claim 11, wherein the first RAT comprises long termevolution (LTE) and wherein the second RAT comprises global system formobile communications (GSM).
 20. A non-transitory, computer accessiblememory medium storing program instructions for performing selectivemeasurement by a user equipment device (UE), wherein the UE comprises afirst radio for communicating using a first radio access technology(RAT) and a second RAT, wherein the program instructions are executableby a processor to: operate the first radio of the UE according to thefirst RAT; operate the first radio according to the second RAT, whereinthe first radio has a lesser frequency of sleep and wake-up cycles whenoperating according to the first RAT than when operating according tothe second RAT, wherein the first radio uses a first clock for each ofthe first RAT and the second RAT when the radio is operating accordingto the first RAT, perform a frequency error estimate (FEE) of the firstclock and adjusting the first clock based on the FEE, wherein performingthe FEE and adjusting the first clock when operating according to thefirst RAT operates to reduce a frequency of the radio performing a FEEand adjusting the first clock when operating according to the secondRAT.